A method of the foregoing type is known from the fundamental U.S. Pat. No. 2,718,690 of John B. Ulam from the year 1955, which itself builds on the landmark U.S. Pat. Nos. 1,392,416 and 2,468,206 from the years 1921 and 1949, respectively, by means of which plated material can be produced, which during the production of objects can be hot and cold worked and deep drawn. In particular, the method involves the uniting of dissimilar metals to form an integral structure which can then be rolled, hammered, forged, drawn, pressed and deep drawn without any risk of the individual layers of the two dissimilar metals coming apart. Although the method according to U.S. Pat. No. 2,718,690 deals with the production of plated composite material in which stainless steel is plated with copper, or copper is arranged between steel layers, the patent states that, instead of this, the composite metal could also be of one and the same metal, i.e. only of stainless steel or only of copper. In this known method no kind of bonding agent is used between the individual metal layers—instead, it is the molecular structures of the metals which unite. The individual metal layers are cleaned by mechanical working so as to remove any oxides, dirt, or the like, from the surfaces. The cleaning, which is done advantageously with a grinding disk, produces a perfectly clean, oxide-free surface. This is necessary in order to expose the molecular lattice structure of the metal. The metal layers are then heated to a suitable temperature so that, under pressure, the adjacent surfaces of the metals can diffuse one into the other.
U.S. Pat. No. 3,210,840 of the same inventor concerns the production of composite metal objects made from aluminum and stainless steel by means of roll-bonding. The metal layers, cleaned and placed one above the other, are reduced in thickness after heat pre-treatment as a result of the rolling by 10 to 35% in order to obtain the mutual diffusion bonding. In the heat pre-treatment stage the metal surfaces are heated to a temperature above the re-crystallization temperature of aluminum but below the melting point of aluminum and below the re-crystallization temperature of stainless steel. The diffusion bonding is achieved by pressing the metal layers together during rolling. (The so-called pressing together described here and in the following can be done by forging or simply by pressing instead of by rolling). In the case of the method known from this US patent, before it is pressed together, the stack of metal layers, arranged one above the other, is first welded at the ends so as to hold the individual component parts of the stack, i.e. the metal layers, firmly in place. During the ensuing rolling operation, as a result of which each of the metal layers is reduced in thickness simultaneously by up to 35%, a very high compressive force must be generated, so that the two outer cover layers of stainless steel also undergo a reduction in thickness by up to 35%. The aluminum layer arranged between the cover layers is also pressurized with this very high compressive force. This is probably one of the reasons why no consideration has yet been given in the state of the art to provide channels in the aluminum layers. The state of the art offers various alternatives to the production of such channels. For example, DE 32 12 768 A1 describes a method for the diffusion welding of structural elements made of a high temperature-resistant metallic material, in particular an oxide dispersion-strengthened nickel-iron alloy. The structural elements can be, for example, the turbine blades of a gas turbine. The structural element is made up of two part elements which are formed in such a way that, after the part elements have been joined together, the finished structural element comprises cooling channels. To form the cooling channels, indentations are milled into the two part elements before they are connected, and it is these which later form the cooling channels. The alloy, from which the structural element is made, is mainly an iron or nickel alloy.
From DE 10 2004 004 459 A1 a method of producing an active cooling panel made from a thermostructural composite material is known. To produce the panel a metallic coating is formed on the inner side of a first part made of a thermostructural composite material which has hollow embosses which form channels and on the inner side of the second part made of a thermostructural composite material which is intended to be laid against the inner side of the first part. The first and second parts are bonded by connecting the inner sides by means of hot isostatic pressing to form a cooling panel with integrated circulation channels. The thermostructural composite materials are normally composite materials of the type carbon/carbon or with a ceramic matrix made of refractory fibers. The metal of the metallic coating which enables the connection by hot pressing, consists of nickel, copper, iron or an alloy of the same, whereby preferentially nickel or a nickel alloy is used.
From DE 32 43 713 A1 a flat heat exchanger panel and a method of manufacturing it are known. The flat heat exchanger panel consists of two superposed plates between which are provided channels for a medium to be heated or cooled. The two plates consist of a metal which is difficult to be plated or which cannot be plated. Between both plates an amorphous metal fixing layer is provided, namely an alloy of nickel, iron or copper, which enables the plates to be bonded by cold rolling. The fixing layer can be a foil which is inserted between the two plates before cold rolling. The two plates are joined to each other by cold rolling only at those places where the fixing layer is located. The metal strips thus bonded are cut up into single panels. Finally, the recessed sections which have not been joined together are widened to form one or more channels in the usual way.
From DE 1 196 045 B a method is known for producing titanium plated aluminum. In it, the base material, aluminum, is laid, together with the titanium sheets or foils to be plated on to it, to form a bundle, and this bundle is then hot rolled. In so doing, the method is executed in such a way that the two materials to be connected only come together just before rolling and the rolling pressure is set such that the thickness of the base material, the aluminum or the aluminum alloy, is reduced by at least 30%. The titanium sheets or titanium foils to be plated on are not heated, but are rolled in a cold state on to the heated aluminum metal, with the aim of avoiding any oxidation of the titanium sheets. A reduction in thickness during rolling of at least 30% must be achieved in order to obtain an effective bonding strength. After production, the plating product is heated to a temperature of between 480 and 565° C. and rolled again in such a way that the reduction in thickness of the base material, i.e. the layer of aluminum or aluminum alloy, is up to 15%. This is designed to further improve the bonding strength between the aluminum and the titanium. Therefore, the total reduction in thickness of the aluminum base material is at least 45%.
Core layers plated with stainless steel and made of one or more aluminum or aluminum alloy layers are nowadays in widespread use in the manufacture of large grilling plates, where a constant grill temperature needs to be maintained irrespective of the volume of food to be grilled which is laid on the grilling plate. In addition, aluminum plated with stainless steel is mainly used in situations where light but corrosion-resistant metals are required, for example for cookware, but also for applications in the aerospace industry.